Polyesters have been produced commercially on a large scale for processing into shaped articles such as fibers, films and bottles, primarily from poly(ethylene terephthalate). Synthetic polyester yarns, for example, have been known and used commercially for several decades, having been first suggested by W. H. Carothers, U.S. Pat. No. 2,071,251, and then Whinfield and Dickson suggested poly(ethylene terephthalate) in U.S. Pat. No. 2,465,319. This polyester polymer has been used most frequently for commercial purposes and has been made from ethylene glycol and from dimethyl terephthalate or terephthalic acid; these polymer precursors have been conveniently reacted together commercially by ester interchange or by direct esterification, respectively, followed by condensation polymerization, generally in multiple stages, with appropriate provision to remove condensation products, such as water, and also excess ethylene glycol that is preferably recycled with removal of unwanted water and by-products, as appropriate, as described in the art, e.g., Edging and Lee, U.S. Pat. No. 4,110,316, MacLean and Estes, U.S. Pat. No. 4,113,704, Goodley and Shiftier, U.S. Pat. No. 4,146,729, and Goodley and Taylor, U.S. Pat. No. 4,945,151.
As indicated, although many polyester polymers (including copolymers) have been suggested, the polyester most widely manufactured and used hitherto for textile fibers has been poly(ethylene terephthalate), which is often referred to as homopolymer. Homopolymer has generally been preferred over copolymers because of its lower cost, and also because its properties have been entirely adequate, or even preferred, for most end-uses. It is known, however, that homopolymer requires special dyeing conditions (high temperature requiring super-atmospheric pressure) not required for nylon fibers, for example. Homopolymer is often referred to as 2G-T.
Poly(ethylene terephthalate/5-sodium-sulfoisophthalate) copolyester has, however, also been manufactured and used commercially in considerable quantities for some thirty years, especially for staple. This copolyester was first suggested by Griffing and Remington in U.S. Pat. No. 3,018,272. A very desirable feature of this copolyester is its affinity for basic (cationic) dyes. Commercially, such copolyester has contained about 2 mole % of the ethylene 5-sodium-sulfo-isophthalate repeat units. Such basic-dyeable copolyester has sometimes been referred to as 2G-T/SSI. This basic-dyeable SSI-containing copolyester has been regarded as important. It has long been highly desirable to make improvements in providing basic-dyeable copolyesters, especially for spinning into filaments for use as textile fibers. As mentioned in our parent U.S. Pat. No. 5,559,205, for making basic dyeable 2G-T/SSI copolyester, we had followed essentially what was taught by Griffing and Remington; we had modified our continuous process of making homopolymer (2G-T) starting from DMT, in that we had added the sodium salt of the dimethylester of 5-sulfoisophthalic acid (5SI) separately into the first vessel 1, in which the ester interchange takes place, manganese acetate (ester interchange catalyst) and antimony trioxide (polymerization catalyst) being fed in as part of the stream of catalyzed glycol (2G), although the antimony trioxide can be added later, and phosphoric acid being added in line 14 to tie up the ester interchange catalyst.
Our parent U.S. Pat. No. 5,559,205 (DP-6335) provides a novel process for preparing sulfonate-modified (basic-dyeable) polyesters of the type originally invented by Griffing and Remington with surprising advantages, especially in avoiding the prior art's reliance on adding an antimony catalyst in the condensation polymerization, and leading to new compositions of matter with improvements in processing and products, including various novel filaments of preferred lithium salt basic-dyeable copolyesters that show advantages over the SSI-containing copolyester filaments that have been available commercially. Thus, we found that lithium 5-sulfo-isophthalic acid glycollate (often referred to herein as LISIPG), which can be written as bis(2-hydroxyethyl)lithium 5-sulfoisophthalate, acts as a polymerization catalyst itself in the preparation of such sulfonate-modified copolyesters, especially if added into homopolymer glycollate (HPG, bis(2-hydroxyethyl)terephthalate) well-mixed with titanium dioxide. This reduces and may even avoid a need for using an antimony polymerization catalyst. Similarly, we found that NASIPG (the corresponding sodium salt glycollate) could be used as a catalyst for making the corresponding sodium salt-containing basic-dyeable copolyesters and textile fibers. Such metal salts may sometimes be referred to herein as a "metal sulfonate salt of a glycollate of isophthalic acid", but are more correctly referred to as a "metal salt of a glycollate of 5-sulfo-isophthalic acid", which latter terminology is used in the claims. As indicated, we have found that the lithium salt-containing basic-dyeable copolyesters have given advantages when used as textile fibers.